This invention relates to a fifth wheel hitch for connection to a kingpin on a truck trailer, and useful on a truck tractor for highway use, or alternatively on stanchions of flatbed railroad cars for off-highway use, i.e. so-called piggyback rail transport.
The basic fifth wheel hitch having an upper bearing plate and a throat to receive a conventional depending kingpin on a trailer is well known. Such a hitch typically employs a set of jaws attached to and forming part of the hitch to receive and connect to a predetermined size kingpin. Most kingpins in the United States are so-called two inch kingpins, having a particular enlarged diameter of about two and thirteen-sixteenths inches at the lower head thereof, and another smaller diameter, namely two inches, at the narrower throat above the head to fit into the cooperatively sized jaws, and typically a body of two and seven-eighths diameter above the throat.
However, not all kingpins are of the two inch size. Some are of three and one-half inch size. In Australia moreover, some three inch kingpins are employed. But fifth wheel hitches are normally manufactured to accommodate only one size kingpin. And, although it is understood that in Europe there has been a hitch which can be converted somehow to accommodate different size kingpins, it is not believed that a fifth wheel hitch which will easily and readily allow substitution of one type of jaw for another has been made heretofore. The capacity to enable quick, easy conversion of the fifth wheel hitch jaws to accommodate different size kingpins, or to allow rapid replacement of worn jaws, would be a significant advantage.
Fifth wheel hitches used on flatbed railroad cars as for piggyback transport of truck trailers normally are mounted on top of a vertically collapsible stanchion. Because fifth wheels are particularly heavy, the elevation and lowering of this weight can present a practical problem. Efforts have been made heretofore to form a fifth wheel of aluminum, namely by casting the fifth wheel plate of aluminum, to achieve lightweight construction. However, the cast aluminum was not of sufficient strength to withstand the stresses normally encountered. Thus, fifth wheel hitches are still of heavy steel construction. Not only is this weight a drawback on collapsible railroad flatbed stanchions, but it also adds considerably to the weight of a conventional truck tractor. Moreover, projected plans for future railroad transport of trailers include use of lightweight flatbed cars weighing only a fraction of today's conventional flatbed cars, to effect less expensive construction and also lighter, more sophisticated wheel bearings. Lowering the weight of the hitches would be desirable to accommodate these lightweight flatbeds.
Conventional fifth wheel hitches include a manual lever or actuator for releasing the kingpin when it is desired to disconnect the trailer. This lever normally projects from one side or the other of the fifth wheel hitch. Hitches employed on railroad flatcars preferably should be releasable by a workman walking along one side or the other of the truck trailers, moving from car to car, thereby enabling a crane to lift the trailers off the railroad cars. For safety reasons, it is inadvisable for the workman to have to move from one side of the railroad cars to the other for this operation. Thus, it would be desirable to have a fifth wheel hitch which would be released from both sides, so that, no matter which side of the flatbeds the worker is walking, he can remain on that side.
Whether the fifth wheel hitch is employed for on-highway or off-highway usage, wear of the jaws renders periodic adjustment advisable to minimize sloppiness of the kingpin in the jaws when connected and under motion. Prior fifth wheel hitches such as those disclosed in U.S. Pat. Nos. 2,663,575 to Ketel and 2,982,566 to Geerds have employed wear adjustment devices, but adjustment has to be made at the inside of the throat of the hitch. Further, such adjustment can only be made when the fifth wheel is detached from the trailer and kingpin. Even then it is cumbersome to do because of minimal space for one's hands at that location, and the presence of grease and dirt. Thus, it would be desirable to have a fifth wheel hitch wherein the adjustment for jaw wear could be made even if the hitch is connected to a kingpin, and from the exterior of the hitch.
In the conventional fifth wheel hitch, the jaws are closed around the kingpin by the entering kingpin itself. It can occur that the kingpin on the trailer is slightly too high relative to the jaws so that the enlarged lower head of the kingpin, rather than the smaller diameter throat thereabove, enters and actuates the jaws to closed position. It is known to employ a lock guard that projects between the jaws and must be shifted down by the kingpin at a correct elevation (see U.S. Pat. No. 2,982,566 at 58), but it would be advantageous to have mechanism preventing a swinging jaw from locking in such a situation and to have this unlocked condition visibly indicated, so that the operator would immediately realize he must change the relative elevation between these components to achieve the effective interengagement with the jaws locking only on the throat of the kingpin.